High molecular weight linear polyesters and copolyesters of terephthalic and isophthalic acid are well known in the prior art. These polymers are described in Whinfield et al, U.S. Pat. Nos. 2,465,319 and Pengilly, 3,047,539 which are hereby incorporated by reference.
The linear polyesters have many desirable properties that make them useful for diverse applications. For certain applications, it is desirable to modify the inherently flammable nature of these polymers so that they are rendered self-extinguishing if they are ignited. In addition, it is desirable to render these polymers non-dripping when burning as the formation of flamming droplets of polymer tends to rapidly propagate fires which cause extensive damage, if not total destruction. Abolins, U.S. Pat. No. 3,671,487 solved this problem by adding to the linear polyester resin, a combination of glass reinforcement, a flame-retardant additive and polytetrafluoroethylene resin. These compositions were flame retardant and non-dripping.
It has now been found that flame retardant, non-dripping polyester compositions may be obtained by adding a flame retardant and polytetrafluoroethylene to a linear polyester resin without any glass reinforcement. Surprisingly, it has been found that these unreinforced compositions require less flame retardant than the glass reinforced compositions of Abolins in order to achieve a flame retardant, non-dripping composition when a minor amount of polytetrafluoroethylene resin is employed in these compositions. For example, the amount of antimony oxide that is used with certain halogenated flame retardants, may be cut in half when a minor amount of polytetrafluoroethylene resin is employed with these compositions. Also, the quantities of polytetrafluoroethylene that are required for providing a non-dripping composition are less than half the amount required by the prior art.
It is, therefore, a primary object of the present invention to provide improved flame retardant, non-dripping linear polyester compositions.
It is also an object of the invention to provide flame retardant, non-dripping linear polyester compositions that include lesser quantities of flame-retardant additives.